Wavelength division multiplexing system and method using reconfigurable diffraction grating

ABSTRACT

The present invention provides an improvement in a wavelength division multiplexer and/or a dense wavelength division multiplexer (WDM/DWDM) by incorporating an electronically reconfigurable diffraction grating ( 108 ). The introduction of the electronically reconfigurable diffraction grating ( 108 ), which is typically fabricated using MEMS (microelectromechanical systems) technology, improves the compact design, durability, and dynamic functionality of the WDM/DWDM system.

FIELD OF THE INVENTION

[0001] This invention relates to the field of wavelength divisionmultiplexing and dense wavelength division multiplexing/demultiplexing,and particularly to the use of reconfigurable diffraction gratings inboth fields.

BACKGROUND OF THE INVENTION

[0002] Wavelength Division Multiplexing (WDM) and Dense WavelengthDivision Multiplexing (DWDM) systems are important components in fiberoptic communication systems and networks. The essential component ofsuch systems focus on the multiplexer/demultiplexer. Currentalternatives include diffractive elements such as dielectric thin filmfilters, arrayed waveguide gratings and fiber Bragg gratings, eachpossessing their own advantages and disadvantages for a particularsystem design. Overall it is desirable in such a system or networkapplication to minimize crosstalk between channels by maximizing channelisolation. This task becomes increasingly more difficult in all fiberDWDM systems where channel spacing and bandwidth is very small. (Pan,Shi, and Loh, WDM Solutions, Laser Focus World Supplement, September1999, pp. 15-18.) Prior art technology is primarily comprised of devicesand systems utilizing the aforementioned diffractive elements, andattention if often given to improving resolution of the system whileminimizing crosstalk by improving other system components such as thefiber optic channels.

[0003] Reconfigurable multiplexing devices can be achieved in a varietyof ways. Several such prior art devices have different levels ofreconfigurability, functionality and performance. For example, U.S. Pat.No. 5,245,681 discloses a reconfigurable wavelength multiplexing devicethat relies on a fiber optic tree structured switching matrix to providethe reconfigurability of the system. The switching matrix is comprisedof several stages of optical couplers that are controlled by theapplication of a specified voltage. The voltage application is used tocontrol the passage of light through the coupler. The ability to turn onand off the voltages to the individual couplers in the matrix make thedevice reconfigurable.

[0004] U.S. Pat. No. 5,550,818 utilizes an optical fiber network ring ina wavelength division multiplexing system. Cross-connecting switchingdevices control the signal routing through the system. Again, theswitches are based on voltage application to the switch.

[0005] U.S. Pat. No. 5,650,835 discloses a reconfigurable opticalbeamsplitter in which periods of optical phase shift regions areestablished across a liquid crystal cell to form an optical grating inthe liquid crystal that will perform as a multiplexing or demultiplexingdevice. The desired pattern of phase shift regions across the cell isaccomplished by applying corresponding voltage differentials across thecell which can be dynamically reconfigured.

[0006] U.S. Pat. No. 5,771,112 provides a reconfigurable device for theinsertion and the extraction of wavelengths utilizing a main opticalswitch connected to a specified number of add/drop multiplexers.

[0007] U.S. Pat. No. 5,712,932 provides a dynamically reconfigurablewavelength division multiplexer. The reconfigurable optical routingsystem is achieved by using fiber-based Bragg grating or a wavelengthselecting optical switch in combination with a fiber optic directionalcoupler.

[0008] All of the above-noted prior art relies primarily on some form ofan optical switch to allow or disallow signal passage through anestablished route in the network or system. However, these systems arelimited in their ability to redirect a specified wavelength through adifferent route in the system. An improvement that enables suchrerouting would have direct application in and benefits to thecommunications industry.

[0009] A key component in a WDM/DWDM system is the means of separatingthe incident light by wavelength. Although there are many means toaccomplish this, recent advances in micromachining technology have ledto the development of reconfigurable diffraction gratings that can beapplied to multiplexing. Such micromachined gratings can be used forvarious electro-optical applications such as multiplexing, spectroscopy,modulated display technology and optical signal processing.

[0010] A deformable grating apparatus is presented in U.S. Pat. Nos.5,459,610 and 5,311,360, both by Bloom et al. An array of beams, atinitially equal heights and with reflective surfaces, are supported atpredetermined fractions of incident wavelength above a similarlyreflective base. Below the base is a means of electrostaticallycontrolling the position of the beams by supplying an attractive forcewhich will deflect all of the beams or every other beam to a secondaryposition. The diffraction of the incident light is dependent upon theposition of the reflective beam elements.

[0011] An electronically programmable diffraction grating is presentedin U.S. Pat. No. 5,757,536 by Ricco, et al. A plurality of electrodescontrol a series of grating elements whose upper surface diffractincident light. The grating is typically formed by a micromachiningprocess.

[0012] Although reconfigurable in nature, the micromachined diffractiongratings discussed above are still limited in their useable bandwidthand the span of available wavelengths for at least the specifiedapplication of lightwave multiplexing and demultiplexing. Ideally, thereconfigurable diffraction grating used should at least permit virtuallyunlimited, dynamic wavelength selection, which the prior art does notpermit.

OBJECTS OF THE INVENTION

[0013] Therefore, it is the object of the invention disclosed herein toprovide an improved wavelength division multiplexer (WDM) using anelectronically reconfigurable diffraction grating.

[0014] It is also an object of the invention to provide an improveddense wavelength division multiplexer (DWDM) using an electronicallyreconfigurable diffraction grating.

[0015] It is also an object of the invention to provide an improvedWDM/DWDM system using an electronically reconfigurable diffractiongrating capable of dynamic reconfigurability of output.

[0016] It is also an object of the invention to provide an improvedWDM/DWDM system capable of simultaneous demultiplexing and opticalswitching functions.

[0017] It is also an object of the invention to provide an improvedWDM/DWDM system capable of demultiplexing input light over an increasedoptical waveband range.

SUMMARY OF THE INVENTION

[0018] The invention disclosed herein in several embodiments provides animprovement in a wavelength division multiplexer and/or a densewavelength division multiplexer (WDM/DWDM) by incorporating anelectronically reconfigurable compound diffraction grating into theoverall multiplexing apparatus or system. The introduction of anelectronically reconfigurable compound diffraction grating, which istypically fabricated using MEMS (microelectromechanical systems)technology, improves the compact design, durability, and functionalityof the WDM/DWDM system.

[0019] In particular, the electronically reconfigurable compounddiffraction grating improves upon alternative wavelength separationtechnology such as dielectric filters, arrayed waveguide gratings, andfiber Bragg gratings, which all limit WDM/DWDM systems regarding channelseparation and channel. The present invention allows individual channelsor wavelengths to be automatically switched between different systemdetectors. The optical switching functions, and also themultiplexing/demultiplexing functions, are both incorporated in a singledevice. This adds tremendous flexibility to an optical network. Thereconfigurable compound diffraction grating has the necessary resolutionto be useful for both WDM and DWDM applications.

[0020] In the preferred embodiment, this optical wavelength divisionmultiplexing apparatus comprises a reconfigurable diffraction gratingdiffracting at least one input light beam into diffracted light beams ofN wavebands wherein N is an integer greater than zero; and furtherdiffracting each of these input light beams into diffracted light beamsacross X diffraction orders wherein X is an integer greater than zero,for each of these N wavebands.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The features of the invention believed to be novel are set forthin the associated claims. The invention, however, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in conjunction with the accompanyingdrawings in which:

[0022]FIG. 1 is a two dimensional cross-sectional schematic view of thewavelength division multiplexer utilizing a reconfigurable diffractiongrating to diffract light to the first order and alternatively to thesecond order.

[0023]FIG. 2 is a top view of the preferred mode of an electronicallyreconfigurable diffraction grating for use in accordance with theinvention.

[0024]FIG. 3 is a two dimensional side view of a deflectable beam andstationary beam in an initial position of one embodiment of thepreferred mode reconfigurable compound diffraction grating for use inaccordance with the invention.

[0025]FIG. 4 is an exploded three dimensional view of one embodiment ofthe preferred mode electronically reconfigurable compound diffractiongrating, in its initial position.

[0026]FIG. 5 is an exploded three dimensional view of one embodiment ofthe preferred mode electronically reconfigurable compound diffractiongrating, in its energized position.

[0027]FIG. 6 is a schematic cross sectional view of an embodiment of thepreferred mode reconfigurable diffraction grating wherein every otherdiffraction beam is deflectable beam with an associated lower electrodeextension beam.

[0028]FIG. 7 is a schematic cross sectional view of another embodimentof the preferred mode reconfigurable compound diffraction gratingwherein every third beam is a deflectable beam with an associated lowerelectrode extension beam.

[0029]FIG. 8 is a schematic cross sectional view of another embodimentof the preferred mode reconfigurable compound diffraction gratingwherein every fifth beam is a deflectable beam with an associated lowerelectrode extension beam.

[0030]FIG. 9 is a schematic cross-sectional view of another embodimentof the preferred mode reconfigurable diffraction grating wherein everybeam is a deflectable beam with an associated lower electrode extensionbeam.

[0031]FIGS. 10 and 11 are representations of light diffracting from asuitable embodiment of the reconfigurable compound diffraction gratingin its initial undeflected position (FIG. 10) and its secondaryenergized position (FIG. 11).

DETAILED DESCRIPTION

[0032] The primary basic function of a wavelength division multiplexeror dense wavelength division multiplexer (WDM/DWDM) is to provide ameans of wavelength separation to a fiber optic communication system ornetwork. Input light is separated into a plurality of channels withtypically narrow width and wavelength separation. Therefore each channelis designated a specific spectral bandwidth that can be detected ormonitored. A dense wavelength division multiplexer is a more specificclass of wavelength division multiplexer in which the channel width andseparation is extremely narrow. The WDM/DWDM can be utilized with avariety of light input sources, typically broadband from a series ofnarrow band sources, or from a single broadband source, introduced fiberoptically to the network. The single most important feature of such asystem is the ability to accurately and precisely separate the incominglight on the receiver end of the fiber into the desired number ofchannels at the specified wavelengths and spectral widths, and also toproperly deliver that light energy to the desired detector or sensor. Asthe light is separated by wavelength, it is important to minimizeinsertion loss and channel crosstalk.

[0033] The present invention provides an improved WDM/DWDM that utilizesa reconfigurable compound diffraction grating. A “compound” diffractiongrating is a diffraction grating which effectively combines andinterleaves two or more grating structures at different positions in thesame physical space, in a way that will become clearer from thedisclosure herein. In addition to multiplexing capabilities, the presentinvention provides for optical switching of the multiple channel outputsbetween at least two different sets of photodetectors. In this way, itessentially combines the function of a WDM and an optical switch into asingle compact device.

[0034]FIG. 1 is a two dimensional operational schematic of the WDM/DWDMaccording to the invention. Optical input means such as fiber 100introduces light source energy into the system. As mentioned above, theinput means 100 is capable of providing light, for example, from aseries of narrowband sources, or from a single broadband source, to thesensor network. The dispersed input source light 102 is collected by afirst system focusing means (e.g., lens) 104 such as the illustratedlens. The first system focusing means 104 is ideally located a focallength away from input means 100 end so as to produce collimated inputlight 106 comprising at least one input light beam which impinges uponthe reconfigurable compound diffraction grating 108. This configurationadds to the efficiency of the system or network by minimizing the numberof optical components in the system and maximizing the energy throughputof the system.

[0035] Reconfigurable compound diffraction grating 108, it will beobserved, is a reflection-type grating where the diffracted output lightemerges from the same side of the grating structure that the input lightenters, as opposed to a transmission-type grating where light enters oneside of the grating structure, is diffracted, and then emerges out theother side.

[0036] As stated above and elaborated below, reconfigurable compounddiffraction grating 108 not only separates light by wavelength formultiplexing, but enables switching among multiple photodetectors byusing various diffractive orders of the diffracted light. The specificoperation of a preferred mode for reconfigurable compound diffractiongrating 108 will be described in detail below, but other less-preferred,yet still suitable grating structures can also be employed within thescope of this disclosure and its associated claims.

[0037]FIG. 1 illustrates reconfigurable compound diffraction grating 108separating collimated input light 106 into only two wavelengths in onlythe first order and second order, just to simplify the drawing. It isunderstood and hereby disclosed, however, that reconfigurable compounddiffraction grating 108 can separate the incoming light into Ndistinctly separate channels. It is also understood and hereby disclosedthat reconfigurable compound diffraction grating 108 can diffract thelight into a single order or multiple orders ranging from the firstorder to X higher orders (the zero order is also available as well).These variables N and X are functions of the design of thereconfigurable compound diffraction grating 108, and will be describedin detail below.

[0038]FIG. 1 thus illustrates a sample, not limiting, situation whereinthe diffraction of light is completely directed to the first order asshown in the solid-line trajectory, or optionally to the second order asshown by the dotted-line trajectory. Again, only the first two ordersare shown for simplicity, but the invention extends into X higher ordersas well. The optical switching between and among the orders, and thusbetween and among various detectors, of all or part of the input light,is a distinct advantage enabled only by the incorporation ofreconfigurable compound diffraction grating 108 into the WDM/DWDM.

[0039] As detailed in FIG. 1, a diffracted light beam of a firstwavelength of a first input light beam is diffracted to first order 110by the reconfigurable compound diffraction grating 108. Similarly, adiffracted light beam of second wavelength of the first input light beamis diffracted to first order 112. Further, reconfigurable compounddiffraction grating 108 similarly diffracts a diffracted light beam ofsaid first wavelength of a second input light beam to first order 114,and a diffracted light beam of said second diffracted wavelength of thesecond input light beam to first order 116. Again, for simplicity, onlytwo input beams and associated diffracted beams are shown in FIG. 1. Itwould be understood by someone of ordinary skill the collimated inputlight 106 is incident on and diffracted from the entire surface of thereconfigurable compound diffraction grating 108 and thus comprisesnumerous input light beams.

[0040] All of the first order diffracted light beams (110, 112, 114, and116) are collectively focused by a first order focusing means (e.g.lens) 118, to a first order, first wavelength output means (e.g. fiber)120 and a first order, second wavelength output means (e.g. fiber) 122.Typically the output means (120 and 122), e.g., fibers, are componentsof a larger first order set of output means 140 such as a first orderoutput fiber array that is coupled to a first order optical detectionmeans 142. This figure is representative of the operation of theinvention, and again, is considered to include N output fibers in theoutput fiber array/bundle, with each fiber corresponding to and carryingone of the N diffracted wavelengths or wavebands. Each wavelength orwaveband is then delivered to one of at least N regions of opticaldetector 142, each said region receiving and detecting that wavelength.

[0041] As stated above, reconfigurable compound diffraction grating 108can also be configured to wholly or partially diffract light into any ofthe higher orders so as to specify wavelengths for individual detectors.In FIG. 1, the alternative of diffracting light into the second order isdemonstrated by the dotted trajectory. This also can be extended intohigher orders, with multiple detectors available to the system, and theseparation by order serving to implement an optical switchsimultaneously with multiplexing by wavelength or waveband.

[0042] Continuing the detailed description of FIG. 1, therefor, thefirst wavelength of the first light beam is also diffracted to secondorder 124, as is the second wavelength of the first light beam alsodiffracted to second order 126. In addition, reconfigurable compounddiffraction grating 108 similarly diffracts the first wavelength of thesecond light beam to second order 128, and the second wavelength f thesecond light beam to second order 130.

[0043] Similarly to what was earlier described for first order, thesecond order input light beams (124, 126, 128, and 130) are collectivelyfocused by a second order focusing means (e.g., lens) 132 to a secondorder, first wavelength output means (e.g. fiber) 134 and a secondorder, second wavelength output means (e.g. fiber) 136. Typically theoutput fibers (134 and 136) are components of a larger second order setof output means 144 such as a second order output fiber array/bundle,coupled to a second order optical detection means 146.

[0044] As stated above, this figure is a simplified representation ofthe operation of the reconfigurable compound diffraction grating 108 inorder to clearly demonstrate the diffraction into wavelengths andorders. It is understood that the reconfigurable compound diffractiongrating 108 is capable of diffracting light along the entire length ofthe grating into any specified order among the X orders, and ofseparating that light into N wavelengths, as determined by its specificdesign. This figure is representative of the operation and the inventionis thus considered to include N output fibers in the output fiberarray/bundle, each fiber corresponding to one the N diffractedwavelengths or wavebands, as well as X optical detection means and Xfiber arrays/bundles, one for each of the X orders.

[0045] The optical components used in FIG. 1 to provide collimated lightinput 106 to reconfigurable compound diffraction grating 108 is a simplefirst system lens 104 placed a focal length away from the input fiber100. Alternatives to the preferred embodiment include more complex meansof collimating optics including multi-element lens systems that providesimilar means of collimation in a more complex design where thepossibility of optical transmission loss needs to be compensated by amore sophisticated lens system.

[0046] The preferred embodiment includes the utilization of outputfibers (i.e. 120, 122, 134, 136), typically as part of a fiber opticarray or bundle (i.e. 140, 144), to collect the individual wavelengthsproduced by the overall system. The use of output fibers minimizes spacerequirements in the multiplexer design and allows easy direction ofindividual or multiple wavelength output to specific optical detectionmeans (i.e. 142, 146).

[0047] In an alternative embodiment, individual optical detectors can beplaced directly at the focus of the first or second order lens (118 or132, respectively) to collect the output directly, and fibers (i.e. 120,122, 134, 136) and fiber bundles (i.e. 140, 144) omitted from FIG. 1.

[0048] Optical detection means (i.e. 142, 146) capture the intensity ofthe individual channels of the WDM/DWDM system. Typically intensitydetectors comprise individual photodiodes, or alternatively detectorarrays such as CCD's or CID's. The optical detection means can be eitheranalog or digital, but primarily serves to measure the intensity of thesignal produced by the individual channels of the system represented bythe individual output fibers.

[0049] Before discussing the details of reconfigurable compounddiffraction grating 108, it is helpful to clarify the use of the terms“wavelength,” “waveband,” and “channel” as used herein. In the art, awaveband is often a light signal comprising one or more wavelengths thatare fairly close to one another, i.e., comprising one or morewavelengths within a given narrow range of wavelengths defining thewaveband. A “channel” is frequently used to describe the carriage of asingle such “waveband” comprising one or more “wavelengths.”

[0050] As used in this disclosure, the term “waveband” is to be broadlyinterpreted and understood as comprising one or more wavelengths closeto one another which are suitable for grouping together in a singlewaveband and carriage over a single channel such as a single fiber.Thus, each of the N “wavelengths” or “wavebands” diffracted at a givenorder by the reconfigurable compound diffraction grating specifiedherein are to be understood and interpreted as comprising one or morewavelengths close to one another, and are not to be understood orinterpreted as comprising only a single wavelength. Thus, a diffractiongrating which diffracts two or more close but distinct “wavelengths”toward a single one of the N optical fibers and/or N detector regions asdisclosed herein, would be considered as diffracting a single wavebandtoward that single optical fiber or detector region.

[0051] In the claims herein, it is to be observed that the term“waveband” is employed throughout, and that this term is to beunderstood and defined as comprising possibly only one wavelength oflight, but alternatively as comprising two or more close but distinctwavelengths of light within a single defined wavelength band.

[0052] It is also to be observed that the foregoing discussion and theclaims refer to N regions of the detectors 142 and 146. It is to beunderstood that detectors, such as photodiodes, are typically unitaryentities and do not have any distinctly defined regions associatedtherewith. There are also detectors that comprise an array of distinctelements or pixels, such as CCD's, whereas these elements could beconstrued as regions of the detector. However, in the present invention,once light has been separated (demultiplexed) into N distinctwavelengths or wavebands as described above, this separated light willbe directed toward and ultimately impinge on a detector. As it impingeson the detector, the light itself in effect defines N regions of thedetector for the present invention by virtue of its N distinctlyseparate wavelengths or wavebands impinging on the detector. That is, agiven single region of the detector comes into being and is defined bythe fact that a given single wavelength or waveband of separated lightis directed to and ultimately strikes upon that given single region ofthe detector, and not by any inherent “regional” property of thedetector itself.

[0053] And finally, it is to be observed that the terms “multiplexing”and “demultiplexing” are typically used in the literature together, asin referring to a multiplexing/demultiplexing system. In a technicalsense, however, multiplexing refers to the combining or splicingtogether of separate wavelengths or wavebands into a single lightsignal, while demultiplexing refers to the splitting of a light signalinto separate component wavelengths or wavebands. Thus, the systemillustrated and described in FIG. 1 is really a demultiplexer in thetechnical sense of that term. However, given the tendency for these twoterms to be used together somewhat interchangeably in the art and in theliterature, and the common and accepted use of “multiplexing system” torefer to a system that demultiplexes multiplexed signals, the term“multiplexing system” is what has been selected to refer in categoricalterms to the invention disclosed herein.

[0054] At this point, we turn to the diffraction grating itself. Theprimary basic function of a diffraction grating in any application is toseparate incident light by wavelength. A diffraction grating in generalis sensitive to the wavelength and input angle of incident light, andits primary operation is to diffract specific wavelengths of light atspecific angles based on the grating design.

[0055] The preferred mode of reconfigurable compound diffraction grating108 used in the preferred embodiment of the invention is shown from atop view in FIG. 2 and exploded cutaway isometric views in FIGS. 4 and5. A base 248, typically made of silicon, supports a frame 250. A lowerelectrode lead 252 lies on the base 248, and runs parallel to and belowthe frame 250, as shown in FIG. 4. An upper electrode lead 254, runsthrough two corners of the frame 250 along the top surface 350 (seeFIGS. 4 and 5) of said frame 250, generally perpendicular to theextension of a set of diffraction beams 256 supported at their ends bythe frame 250.

[0056] In one set of embodiments, this set of diffraction beams 256comprises both stationary beams 358 and deflectable beams 360, as shownin FIGS. 3 through 8. In another embodiment, shown in FIG. 9, all of thediffraction beams 256 are deflectable beams 360. In all embodiments,diffraction beams 256 run substantially parallel to each other andsubstantially perpendicular to the sides of the frame 250, by which theyare supported. Diffraction beams 256 are of substantially uniformthickness, width and length. Diffraction beams 256 are much longer thanthey are wide and thick, and are spaced along frame 250 at periodicintervals. Both the base 248, and the top surface of the set of beams256, are of a reflective nature.

[0057] The upper electrode lead 254, the top surface 350 of the frame250, and the set of beams 256 are all electrically connected, andtogether comprise an upper electrode. The lower electrode lead 252 and aseries of lower electrode extension beams 362 are all electricallyconnected, and together comprise a lower electrode. The frame 250, whichis an electrical insulator, enables the introduction of voltagedifferentials between the upper electrode comprising 254, 350 and 256,and the lower electrode comprising 252 and 362.

[0058] The deflectable beams 360 can be identified as those in the setof beams 256 which have the lower electrode extension beams 362 runningunderneath them. Also, in their initial undeflected position shown inFIG. 4 (see also FIGS. 6 through 9), the deflectable beams 360 are in anelevated plane above the stationary beams 358, although remaininggenerally parallel thereto. The relative parallelism is achieved by theexcessive length of all of the beams 256 as compared to their length andwidth. This elevation of the deflectable beams 360, and in particularthe reconfigurable, compound nature of this grating, is a key designfeature in of reconfigurable compound diffraction grating 108, which canbe viewed as the “compound” superposition of two grating structures. Theseries of deflectable beams 360, comprise a low resolution gratingsecondary to the higher resolution primary grating consisting of thefull set of beams 256.

[0059] In the embodiment of FIGS. 2 through 8, the “compound”superposition of this grating structure is built in by theprefabrication of elevated deflectable beams 360 having lower electrodeextension beams 362 running underneath them, and of stationary beams 358defining a plane slightly below that of deflectable beams 360 and nothaving any lower electrode extension beams 362 associated therewith. Inthe embodiment of FIG. 9, which will be elaborated further below, all ofthe beams are deflectable beams 360, there are no stationary beams 358,and the “compound” structure wherein one set of beams is elevated withrespect to another set of beams is achieved by applying a voltagedifferential to one set of beams while applying different voltagedifferentials (or no voltage differentials) to other sets of beams. Inall embodiments, the system is reconfigured, at will, by a suitableapplication of voltage differentials to suitable set of diffractionbeams 256. The embodiment of FIG. 9 is the most general, for so long asthe voltage differential that can be applied to each diffraction beam256 is individually controllable, the overall grating structure can beactively reconfigured in any chosen manner whatsoever.

[0060] Thus, in FIGS. 2 through 8, the diffraction of incident light byreconfigurable compound diffraction grating 108 is controlled bymanipulating the vertical position of particular individual beams in theset of beams 256, and in particular, by changing the vertical positionof the deflectable beams 360 while leaving unaltered the verticalposition of the stationary beams 358. In FIG. 9, this is achieved bychanging the vertical position of one set of beams, while leaving thevertical position of other sets of beams unaltered or differentlychanged.

[0061]FIG. 3 shows a cutaway side view of the interior of reconfigurablecompound diffraction grating 108 in which the vertical elevation of theplane of the deflectable beams 360, over the plane of the stationarybeams 358 is evident. One of the lower electrode extension beams 362 isshown lying on the base 248, immediately beneath one of the deflectablebeams 360. This deflectable beam 360 is shown in its initial position.As seen in FIG. 3, the majority of the top surface of the deflecteddeflectable beam 360, remains substantially parallel to an adjacentstationary beam 358. Application of a voltage differential between thedeflectable beams 360, and the lower electrode extension 362, results ina deflection of the beams 360, in which they approach the plane of thestationary beams 358. Of course, application of different voltages wouldresult in different degrees (distances) of deflection.

[0062]FIG. 4 is a cutaway isometric view of the reconfigurable compounddiffraction grating 108 in an initial, undeflected position. This viewshows exactly how the lower electrode extension beams 362 project alongthe base 248 from the lower electrode lead 252, and how the deflectablebeams 360 are positioned directly above the lower electrode extensionbeams 362 so that they may be deflected when a voltage differential isapplied between the upper and lower electrodes generally.

[0063]FIG. 5 is a similar cutaway isometric view of the reconfigurablecompound diffraction grating 108, with the deflectable beams 360depicted at a deflected position in which the deflectable beams 360 arein the same plane as the stationary beams. Applying a voltagedifferential across the two (upper and lower) electrodes via the upperand lower electrode leads 254 and 252, respectively, causes thedeflectable beams 360 to move towards the lower electrode extensionbeams 362. The deflection of the deflectable beam 360, is proportionalto the voltage applied to the lower electrode lead 252, and therefore tothe lower electrode extension beam 362 electrically connected thereto.The upper electrodes (comprising 254, 350, and 256 (i.e., 358/360)) aretypically fabricated as a unit whole with the rest of the gratingstructure typically of a material such as silicon. No shielding isnecessary between the stationary beams, 358, and the adjacentdeflectable beams, 360, since the aspect ratio of the set of beams, 256,is such that voltage applied to the lower electrode lead 252, andtherefore to the lower electrode extension beam, 362, is enough to onlydeflect the deflectable beam, 360.

[0064] Thus far, the stationary beams 358, and the deflectable beams 360have been shown alternating every position in the diffraction grating,which is represented in the cross sectional schematic view of FIG. 6.Alternative configurations of the stationary beams 358, and thedeflectable beams 360, may be desired depending on desired wavelengthrange. Although the diffraction of the incoming light is altered bychanging the vertical position of the deflectable beams 360, and therebychanging the vertical spacing between the stationary beams 358, and thedeflectable beams 360, alternative configurations of the stationarybeams 358 and the deflectable beams 360 are beneficial for various partsof the spectrum. In addition, such configurations can be determinedbased on the resolution requirements of the secondary grating structurethat comprises the deflectable beams 360.

[0065]FIG. 7 illustrates an alternative configuration in which thedeflectable beams 360 occupy every third position and the stationarybeams 358 occupy the remaining positions. Similarly, FIG. 8 illustratesanother alternative configuration in which the deflectable beams 360occupy every fifth position and the stationary beams 358 occupy theremaining positions. The alternative configurations are not limited tothose shown in

[0066]FIGS. 6, 7, and 8, and indeed, any repetitive periodic patterncould be incorporated into the grating design by someone of ordinaryskill and is contemplated by this disclosure and its subsequentassociated claims. From these configurations, the diffraction of theincoming light is controlled by the vertical position of the deflectablebeams 360. Generally speaking, FIGS. 6 though 8 respectively, a subsetplurality the diffraction beams, namely deflectable beams 360, can beseparated from one another by exactly one, two and four diffractionbeams of another subset plurality, namely stationary beams 358, of thediffraction beams, simply by virtue of the basic grating structureconfiguration.

[0067]FIG. 9, shows another alternative configuration of thereconfigurable compound diffraction grating 108 that could be beneficialto the design of the WDM/DWDM system, and which in fact is the mostgeneral. This employs a lower electrode extension beam 362 under everybeam in the set of beams 256, thereby making every beam a deflectablebeam 360, wherein some of the beams 256 are voltage deflected to aposition appropriate to stationary beams 358, while others are voltagedeflected to a position appropriate to deflectable beams 360, as earlierdescribed. With this design, the voltage applied to the lower electrodeleads 252 can be controlled to individually address each lower electrodeextension 362 to actively reconfigure the diffraction grating to theappropriate configuration (every other, every third, every fifth, etc.)for the specified wavelength distribution to appropriate detectors ofthe WDM/DWDM. Here, a subset plurality the diffraction beams can beseparated from one another by exactly one, two, four, and indeed anynumber of diffraction beams of another subset plurality of thediffraction beams, by virtue of the voltage differentials applied.

[0068] Aside from complete control over the periodicity, theconfiguration of FIG. 9 also enables three-level, four-level, and indeedmultilevel compound grating structures to be achieved by applying anumber of different voltage differentials to different selected sets ofbeams 256. Indeed, if each electrode pair is individually addressable,then the grating of FIG. 9 can be reconfigured into any periodic andcompound configuration desired. This embodiment is especially applicableto a WDM/DWDM in which the input light is diffracted into more than twoorders simultaneously.

[0069] Thus, in the embodiment of FIG. 9, each diffraction beam has onelower electrode extension beam associated therewith. This enables atleast one subset plurality of the diffraction beams to be moved from theinitial position thereof to the deflected position thereof in anydesired periodic combination with respect to at least one other subsetplurality of the diffraction beams (reconfigurable periodicity). Itfurther enables the deflected positions of at least one subset pluralityof the diffraction beams to differ from the deflected positions of atleast one other subset plurality of the diffraction beams(reconfigurable compound structure).

[0070] In short, in its most general form, the embodiment of FIG. 9 usesvoltage differential application means enabling the application of aplurality of voltage differentials to be applied to a correspondingplurality of subsets of the diffraction beams, wherein these subsets canbe as small as a single beam, enabling full periodic and compoundreconfigurability. (This “individual voltage addressability” of thebeams is most suited to the FIG. 9 embodiment, but can also be utilizedwith other embodiments as well.) This advanced design is a naturalextension of the configurations of the reconfigurable compounddiffraction grating 108 presented herein and allows a singlereconfigurable compound diffraction grating to satisfy all possibleconfiguration requirements of the WDM/DWDM system.

[0071] Using as an example the configuration in which every third beamis deflectable as in FIG. 7 (or in which the embodiment of FIG. 9 hasvoltages applied to it so as to configure an every-third-beamstructure), FIGS. 10 and 11 are respective representations of the lightdiffracted from the reconfigurable compound diffraction grating 108 inthe initial position (FIG. 10) and as the beams are deflected to thesecondary position where the deflected and stationary beams are aligned(FIG. 11). That is, FIG. 10 represents the initial position of FIG. 4,and FIG. 11 represents the secondary position of FIG. 5, but with theevery-third-beam spacing of FIG. 7. The diffraction is changed when thebeams are deflected due to the change in the position of the reflectivesurface. The purpose of these representations is to demonstrate thereconfigurability and operation of the reconfigurable compounddiffraction grating used to achieve the switching and wavelength orwaveband selection described for the WDM/DWDM in FIG. 1, and not in anyway to limit the disclosure or the associated claims.

[0072]FIG. 10 shows in detail, the light diffracted from thereconfigurable compound diffraction grating base 248 in the initialposition of the configuration wherein every third beam is deflectable.The secondary diffraction grating comprising only the deflectable beams360 causes the diffraction described below as due to 3 d spacing. Theprimary diffraction grating consisting of the entire set of beams 256,accounts for the diffraction described below as due to d spacing. Thediffraction capable of being generated from impinging light 1064 (whichcorresponds to one of the input light beams discussed in connection withFIG. 1), includes a zero order, 1066, a first order (due to 3 d spacingwhere d is beam spacing), 1068, a second order (due to 3 d spacing),1070 and a third order/first order superposition (due to 3 d spacing andd spacing, respectively), 1072. In this example, the first order 1068represents and correspond to first orders 110, 112, 114, and 116 ofFIG. 1. Similarly, second order 1070 represents and correspond to secondorders 124, 126, 128, and 130. FIG. 11 shows the diffraction generatedfrom the grating base 248 when the deflected beams (every third beamconfiguration) are moved to their secondary position where they arealigned with the undeflected beams. In this configuration impinginglight 1064 is concentrated in only the zero order, 1066 and first order(due to d spacing), 1072. It is important to note that FIGS. 10 and 11are simply illustrative of how light readings may be taken from thisgrating, and that many other variations obvious to someone of ordinaryskill are possible and clearly within the scope of this disclosure andits associated claims.

[0073] The reconfigurable compound diffraction grating 108 is typicallyfabricated using MEMS processing. Current MEMS processing techniques arecapable of features on the scale of 1-2 microns. The most criticaldimension in the operation of the diffraction grating is the width ofthe beam. The ruling or grating spacing determines the resolution of thegrating. With the current feature sizes on the 1-2 micron scale, agrating comparable with a medium resolution (600-1200 grooves/mm)conventional optical grating is produced. This resolution is ideal forthe visible and near-infrared region of the electromagnetic spectrum andhigher wavelengths, as well. The design of the reconfigurable compounddiffraction grating can be scaled to include wider beams and gratingspacings to be useful in applications in the infrared region of theelectromagnetic spectrum. As the size limitations of the MEMS processingtechnique decreases, the reconfigurable compound diffraction gratingwill be applicable to even shorter wavelengths, and it is contemplatedthat the scaling of the beam width and ruling to such smaller dimensionsis fully encompassed by this disclosure and its subsequent associatedclaims.

[0074] Alternative embodiments of the present invention of the WDM/DWDMsystem primarily utilize alternative configurations of reconfigurablediffraction grating 108. The design of the reconfigurable diffractiongrating presented in FIGS. 2 through 9 constitutes the best modepossible at present. However, alternative configurations of thereconfigurable diffraction grating that can be implemented in theWDM/DWDM system include variations in the configuration of beams thatestablish the rulings of the diffraction grating. The design presentedin the preferred embodiment of the WDM/DWDM system can be formed with avariety of beam widths and spacings between the beams, also known asgrating spacing. For example, these variations include but are notlimited to, beams spaced half a beam width apart, a quarter of a beamwidth apart, and twice a beam width apart. All such variations in thereconfigurable diffraction grating, and similar variations, arecontemplated by this disclosure and its associated claims.

[0075] Further, while the reconfigurable compound diffraction grating108 illustrated and discussed in detail in FIGS. 2 through 9 is the bestmode for compound diffraction grating 108 that can be used incombination with the multiplexer of FIG. 1, the use of any otherdiffraction grating known in the art possessing suitable size andoperational characteristics for use as element 108 in combination withthe overall multiplexing system shown in FIG. 1 is also fullycontemplated within the scope of this disclosure and its associatedclaims. This could include, for example, not limitation, any of thevarious diffractive elements referred to in the background of theinvention herein, as well as the diffractive elements disclosed in theseveral U.S. Patent referred to herein, to the extent that theiremployment for this multiplexing application may be feasible and useful.

[0076] That is, this disclosure and its associated claims broadlyencompass both a lightwave multiplexing system employing any suitablereconfigurable compound diffraction grating as element 108 in the mannerand combination disclosed in FIG. 1, as well as, more narrowly, alightwave multiplexing system employing the specific best mode of thereconfigurable compound diffraction grating disclosed in FIGS. 2 through9 as element 108 in combination with the overallmultiplexing/demultiplexing system disclosed in FIG. 1.

[0077] Another alternative configuration of the reconfigurablediffraction grating 108 that could be beneficial to the design of theWDM/DWDM system for a specific implementation includes coating the setof beams 256, the upper electrode lead 254, and the lower electrode lead252, with a thin film of reflective coating such as gold or aluminum inorder to significantly increase the reflectivity and therefore resultantsignal strength. Coating the top surface of the set of beams 256, alsoprovides a means of reducing the electrical resistance. This isparticularly important in high frequency applications.

[0078] While only certain preferred features of the invention have beenillustrated and described, many modifications, changes and substitutionswill occur to those skilled in the art. It is, therefore, to beunderstood that this disclosure and its associated claims are intendedto cover all such modifications and changes as fall within the truespirit of the invention.

I claim:
 1. An optical wavelength division multiplexing system,comprising: a reconfigurable diffraction grating (108) diffracting atleast one input light beam (106) into diffracted light beams of Nwavebands (110, 112, 114, 116) wherein N is an integer greater thanzero; and further diffracting each of said input light beams (106) intodiffracted light beams (110, 112, 114, 116) across X diffraction orderswherein X is an integer greater than zero, for each of said N wavebands;wherein: N is greater than one.
 2. The system of claim 1, furthercomprising: at least X sets of at least N light output means (120, 122)each, each one of said X sets corresponding with one of said Xdiffraction orders, and for each said diffraction order, each one ofsaid N light output means (120, 122) corresponding with one of said Nwavebands at said order, wherein: for each given one of said Xdiffraction orders, all of the diffracted light beams (110, 112, 114,116) of a given one of said N wavebands, from all of said input lightbeams (106), are focused on the one of said N light output means (120,122) corresponding with said given waveband within the one of said Xsets of output means corresponding with said given one of said Xdiffraction orders.
 3. The system of claim 1 or claim 2, saidreconfigurable diffraction grating (108) comprising: a first pluralityof substantially parallel diffraction beams (256); a second plurality oflower electrode extension beams (362) each associated with,substantially parallel to, and beneath one of said diffraction beams(256), said second plurality being at most equal to said first pluralityin number; and voltage differential application means (252) for applyingselected voltage differentials between each of said lower electrodeextension beams (362) and its associated diffraction beam (256) tothereby move at least one diffraction beam (256) from an initialposition thereof to a deflected position thereof.
 4. The system of claim3, said voltage differential application means enabling the applicationof a plurality of voltage differentials to applied to a correspondingplurality of subsets of said diffraction beams (256), said subsets ofsaid diffraction beams (256) comprising at least one of said diffractionbeams (256).
 5. The system of claim 1 or claim 2, further comprising areflective coating on upper surfaces of a plurality of diffraction beams(256) of said reconfigurable diffraction grating (108) and on at leastan upper surface of a base (248) of said reconfigurable diffractiongrating (108).
 6. The system of claim 1 or claim 2, wherein saidreconfigurable diffraction grating (108) is fabricated usingmicroelectromechanical systems technology.
 7. The system of claim 1 orclaim 2, wherein a ratio of spacing between each successive diffractionbeam of a plurality of diffraction beams (256) of said reconfigurablediffraction grating (108) to a width of each said diffraction beam (256)is substantially between ¼ to 1 and 2 to
 1. 8. The system of claim 1 orclaim 2, further comprising: optical input means (100) for delivering aninput source light beam (102) to said system; and means of collimating(104) said input source light beam (102) into said at least one inputlight beam (106) diffracted by said reconfigurable diffraction grating(108).
 9. The system of claim 2, each of said at least N output means(120, 122) of each said set of output means (140) comprising anindividual optical fiber.
 10. The system of claim 2, each of said atleast X sets of at least N light output means (140) comprising anoptical fiber bundle of at least N optical fibers.
 11. The system ofclaim 1, further comprising: at least X optical detectors (142, 146),each one of said X optical detectors (142, 146) corresponding with anddetecting diffracted light (110, 112, 114, 116) from one of said Xdiffraction orders, wherein: for each given one of said X diffractionorders, all of the diffracted light beam (110, 112, 114, 116) at saidgiven diffraction order, from all of said input light beams (106), arefocused on the optical detector (142) corresponding with said givendiffraction order; and for each given one of said X diffraction orders,all of the diffracted light beams (110, 112, 114, 116) of a given one ofsaid N wavebands, from all of said input light beams (106), are focusedon one of at least N light output regions (120, 122) of the opticaldetector (140) corresponding with said given diffraction order.
 12. Thesystem of claim 2, further comprising: at least X optical detectors(140, 146), each one of said X optical detectors (140, 146)corresponding with and detecting diffracted light (110, 112, 114, 116)from one of said X diffraction orders, and also corresponding with andreceiving diffracted light from the set of at least N light output means(140) corresponding with said one of said X diffraction orders, wherein:for each given one of said X diffraction orders, all of the diffractedlight beams (110, 112, 114, 116) at said given diffraction order, fromall of said input light beams (106), are received by the opticaldetector (142) corresponding with said given diffraction order over saidset of at least N light output means (120, 122) corresponding with saidgiven diffraction order; and for each given one of said X diffractionorders, all of the diffracted light beams (110, 112, 114, 116) of agiven one of said N wavebands, from all of said input light beams (106),are received by one of at least N light output regions (120, 122) of theoptical detector (142) detecting said given diffraction order over theone of said N light output means (120, 122) corresponding with saidgiven one of said N wavebands at said order.
 13. The system of claim 1or claim 2, wherein X is greater than one and said X diffraction ordersinclude at least one diffraction order other than a first diffractionorder of said reconfigurable diffraction grating (108).
 14. A method ofoptical wavelength division multiplexing, comprising the steps of:diffracting at least one input light beam (106) into diffracted lightbeams (110, 112, 114, 116) of N wavebands wherein N is an integergreater than zero, using a reconfigurable diffraction grating (108); andfurther diffracting each of said input light beams (110, 112, 114, 116)into diffracted light beams across X diffraction orders wherein X is aninteger greater than zero, for each of said N wavebands, also using saidreconfigurable diffraction grating (108); wherein: N is greater thanone.
 15. The method of claim 14, comprising the further steps of:providing at least X sets of at least N light output means (140) each,each one of said X sets corresponding with one of said X diffractionorders, and for each said diffraction order, each one of said N lightoutput means (140) corresponding with one of said N wavebands at saidorder; and for each given one of said X diffraction orders, focusing allof the diffracted light beams (110, 112, 114, 116) of a given one ofsaid N wavebands, from all of said input light beams (106), on the oneof said N light output means (140) corresponding with said givenwaveband within the one of said X sets of output means (140)corresponding with said given one of said X diffraction orders.
 16. Themethod of claim 14 or claim 15, comprising the father steps of:providing a first plurality of substantially parallel diffraction beams(256) of said reconfigurable diffraction grating (108); providing asecond plurality of lower electrode extension beams (362) or saidreconfigurable diffraction grating (108), each associated with,substantially parallel to, and beneath one of said diffraction beams(256), said second plurality being at most equal to said first pluralityin number; and moving at least one said diffraction beam (256) from aninitial position thereof to a deflected position thereof by applyingselected voltage differentials between said diffraction beams (256) andtheir associated lower electrode extension beams (362), using voltagedifferential application means (252).
 17. The method of claim 16,comprising the further step of applying a plurality of voltagedifferentials to a corresponding plurality of subsets of saiddiffraction beams (256), said subsets of said diffraction beams (256)comprising at least one of said diffraction beams (256), using saidvoltage differential application means (252).
 18. The method of claim 14or claim 15, comprising the further step of: providing a reflectivecoating on upper surfaces of a plurality of diffraction beams (256) ofsaid reconfigurable diffraction grating (256) and on at least an uppersurface of a base (248) of said reconfigurable diffraction grating(108).
 19. The method of claim 14 or claim 15, comprising the furtherstep of: fabricating said reconfigurable diffraction grating usingmicroelectromechanical systems technology.
 20. The method of claim 14 orclaim 15, wherein a ratio of spacing between each successive diffractionbeam of a plurality of diffraction beams (256) of said reconfigurablediffraction grating (108) to a width of each said diffraction beam (256)is substantially between ¼ to 1 and 2 to
 1. 21. The method of claim 14or claim 15, further comprising: delivering an input source light beam(102) for multiplexing by said method, using optical input means (100);and collimating said input source light beam (102) into said at leastone input light beam for diffracting (106) by said reconfigurablediffraction grating (108).
 22. The method of claim 16, each of said atleast N output means (120, 122) of each said each said set of outputmeans (140) comprising an individual optical fiber.
 23. The method ofclaim 16, each of said at least X sets of at least N light output means(140) comprising an optical fiber bundle of at least N optical fibers.24. The method of claim 16, comprising the further steps of: providingat least X optical detectors (142, 146), each one of said X opticaldetectors (142, 146) corresponding with and detecting diffracted light(110, 112, 114, 116) from one of said X diffraction orders; for eachgiven one of said X diffraction orders, focusing all of the diffractedlight beams (110, 112, 114, 116) at said given diffraction order, fromall of said input light beams (106), on the optical detector (142)corresponding with said given diffraction order, and for each given oneof said X diffraction orders, focusing all of the diffracted light beams(110, 112, 114, 116) of a given one of said N wavebands, from all ofsaid input light beams (106), on one of at least N light output regions(120, 122) of the optical detector (142) corresponding with said givendiffraction order.
 25. The method of claim 16, comprising the furthersteps of: providing at least X optical detectors (142, 146), each one ofsaid X optical detectors (142, 146) corresponding with and detectingdiffracted light (110, 112, 114, 116) from one of said X diffractionorders, and also corresponding with and receiving diffracted light (110,112, 114, 116) from the set of at least N light output means (140)corresponding with said one of said X diffraction orders; for each givenone of said X diffraction orders, receiving all of the diffracted lightbeams (110, 112, 114, 116) at said given diffraction order, from all ofsaid input light beams (106), with the optical detector (142)corresponding with said given diffraction order, over said set of atleast N light output means (140) corresponding with said givendiffraction order; and for each given one of said X diffraction orders,receiving all of the diffracted light beams (110, 112, 114, 116) of agiven one of said N wavebands, from all of said input light beams (106),at one of at least N light output regions (120, 122) of the opticaldetector (142) detecting said given diffraction order, over the one ofsaid N light output means (140) corresponding with said given one ofsaid N wavebands at said order.
 26. The method of claim 14 or claim 15,wherein X is greater than one and said X diffraction orders include atleast one diffraction order other than a first diffraction order of saidreconfigurable diffraction grating (108).
 27. The system of claim 1 orclaim 2, said at least one input light beam comprising more than oneinput light beam.
 28. The system of claim 13, said at least one inputlight beam comprising more than one input light beam.
 29. The method ofclaim 14 or claim 15, said at least one input light beam comprising morethan one input light beam.
 30. The method of claim 26, said at least oneinput light beam comprising more than one input light beam.